Look at the 3 piece 90, 1C on the chart which is essentially what you make with a couple 45s. It has a resistance of 61', 48', 39'. So the best you'll get if there is some space between them will be 39' but perhaps more because there are the 4 ridges where each pipe to elbow joint is.
I've been looking at PVC for my system (CV-Max) but here we can't get much DWV in 6" and nothing in 8". Only Schedule 40 which is $10' for 6" pipe and $16 for 8" and that was the best I could locate. Spiral pipe starts at $3.50' for 6" and that's more than I would prefer to spend. Nothing for the cheapskate.